In order to align the blade of a power saw with a cutting line on a workpiece, the operator must typically bring the blade into contact with the workpiece to determine if the saw is properly aligned with the cutting line. As is familiar to those skilled in the art, it may be necessary to repeat this procedure several times in order to achieve proper alignment for precision cutting. This procedure is time consuming, and the desired precision is often not achieved, resulting in wasted time and materials.
Moreover, circular saw blades have a discrete width. If the blade is centered over the cutting line, more material than required will be removed. For example, if the blade is centered directly over the cutting line, the cut in the workpiece will be inaccurate by an amount approximately equal to half the width of the blade. The cutting line, which is generally a pencil mark, or scribe mark on the workpiece, also has a discrete width, further complicating alignment. Consequently, it is often difficult to determine precisely where the blade will engage the cutting line.
U.S. Pat. No. 4,257,297, issued to Nidbella on Mar. 24, 1981 discloses a power saw where the blade is interposed between an incandescent bulb and the workpiece. The blade interrupts the light and casts a shadow onto the workpiece generally showing the edges of the blade. However, circular blades are typically out of flatness by 0.005-0.015", causing the shadow to inaccurately reflect where the blade will engage the workpiece. Moreover, the teeth on circular blades are often angled away from the plane of the blade, creating a jagged-edged shadow. This drawback is also present in blades having carbide tips wider than the body of the blade. Therefore, the overall accuracy of shadow system is inadequate for precision woodworking.